1. Technical Field of the Invention
The present invention relates to a seismic isolation device, and more particularly to a seismic isolation device mounted between an upper structure of a bridge constructed by engineering work and a building, etc, and a substruction or a lower structure thereof, to suppress shake of the upper structure against an earthquake.
2. Description of the Related Art
Conventionally, various sorts of seismic isolation devices have been proposed. The devices are provided with friction plates arranged so as to be laminated in a hollow part vertically formed through a laminated rubber body, and supports vertical load of an upper structure, and provides attenuation by frictional force between the friction plates when horizontal deformation arises by an earthquake or the like.
For example, the patent document 1 describes a seismic isolation structure comprising a complex laminated body, and a laminated body that are held in parallel between an upper surface plate and a lower surface plate. In the complex laminated body, hard plates with rigidity and elasticity plates with viscoelasticity are laminated one after the other, and in the laminated body, and friction plates such as metallic plates coated with a plurality of high molecular compounds are laminated.
In addition, a seismic isolation structure is described in the patent document 2. In the seismic isolation structure, twenty copper plates as hard plates and twenty one rubber plates as soft plates are alternately laminated between an upper surface plate and a lower surface plate, and forty three friction plates made of unsaturated polyester resin reinforced by glass fiber are laminated, and those are enclosed in a hollow part provided in the central portion of the laminate body part. In the seismic isolation structure, an iron plate is arranged as a presser plate on the laminated body of the frictional plates; an upper cover to which a female thread is screwed is disposed at the central portion thereof; the upper cover is fastened with a torque of 150 kg-cm to apply charging force to the friction-plates-laminated body; and the charging force is adjustable through torque to the upper cover.
Further, the patent document 3 proposes a base isolation support device that comprise: a flexible support body in which elastomer layers such as rubber and middle rigidity plates are vertically laminated and adhered one after the other; a slide plates lamination body in which a plurality of slide plates consisting of at least one of iron alloy, copper or its alloy, polytetrafluoroethylene, and graphite are vertically laminated so as to slidable with each other. The slide plates lamination body is arranged so as to be enclosed by the flexible support body, and the two bodies cooperatively support load, and some of the slide plates of the slide plates lamination body are made of material of which friction coefficient differs from that of other slide plates.
Since these devices according to the above inventions have a constant height of the laminated friction plates, they are preferred for lightweight structures such as single houses for instance, against secular changes arising in the laminated rubber body, as a means for inhibiting a creep phenomenon that vertical displacement gradually decreases, or a means for suppressing a vertical subduction phenomenon at the time of horizontal deformation of the laminated rubber body. On the other hand, in case that the load supported by the seismic isolation device is large, excessive vertical load acts on the friction plates or friction plate mounting parts, which may cause a change in their friction characteristic, breakage of the friction plates, and also breakage of the seismic isolation device itself.
Then, focusing to the action of the vertical subduction at the horizontal deformation of the laminated rubber body, a technology for preventing excessive vertical load from acting on the friction plates is proposed. In this technology, shock absorbing material is mounted above and/or below the friction plates laminated in the hollow part of the laminated rubber body.
For example, the patent document 4 proposes a seismic isolation device that comprises: a laminated rubber body in which rubber plates and metal plates are adhered one after the other, and a throughhole is prepared in a direction vertical to surfaces of the laminated plates; flanges adhered to the both end faces of the laminated rubber body: a plurality of friction plates laminated in the throughhole of the laminated rubber body; and an elastic member to which precompression for vertically pressing the friction plates is applied.
In addition, a seismic isolation device for light weight construction is proposed in the patent document 5. In the seismic isolation device, between a pair of mounting plates are laminated reinforcing plates and elasticity plates one after the other; these mounting plates and elasticity plates, and these elasticity plates and reinforcing plates are respectively adhered with each other to form a seismic isolation device main body; through the main body is drilled a hole for attenuating vibration penetrating at least the reinforcing plates and the elasticity plates; in the hole are disposed low resiliency members with low strength and rigid plate-like bodies are laminated one after the other; a clearance is formed between an outer peripheral portion of each low resiliency member and a face constituting the hole; and the plate-like bodies are slidable with each other.
Further, the patent document 6 proposes a seismic isolation device, which comprises: a laminated part in which rubber-like elasticity layers and rigid plate layers are alternately laminated in a vertical direction; a throughhole vertically passing through the laminated part; and a plurality of friction plates enclosed in the throughhole with a state that the plates are laminated, and the device is characterized in that seizure of the friction plates between them and changes in friction coefficient accompanied by the seizure can be suppressed, and stable seismic isolation effect may be obtained.
Patent document 1: Japanese Patent Publication Heisei 8-105123 gazette
Patent document 2: Japanese Patent Publication Heisei 9-296845 gazette
Patent document 3: Japan Patent 3717287 gazette
Patent document 4: Japanese Patent Publication Showa 62-141330 gazette
Patent document 5: Japan Patent 2990532 gazette
Patent document 6: Japanese Patent Publication 2000-283229 gazette